Well drilling is a process used in penetrating subterranean zones (also known as subterranean formations) that produce oil and gas. In well drilling, a well bore is drilled while a drilling fluid (also known as a drilling mud) is circulated through the well bore. The circulation of the drilling fluid is then terminated, and a string of pipe, e.g., casing, is run in the well bore. The drilling fluid in the well bore is conditioned by circulating it downwardly through the interior of the pipe and upwardly through the annulus, which is located between the exterior of the pipe and the walls of the well bore. Next, primary cementing is typically performed whereby a slurry of cement in water is placed in the annulus and permitted to set into a hard mass to thereby attach the string of pipe to the walls of the well bore and seal the annulus.
Drilling through subterranean zones containing clay and shales which swell upon exposure to water requires the use of non-aqueous drilling fluids to avoid problems such as sloughing and well collapse. Such non-aqueous fluids include a base fluid, e.g., diesel, mineral oil, unsaturated olefins, organic esters, or a combination thereof. Other components, such as calcium chloride brine, emulsifying surfactants, rheology modifiers, and wetting agents, are added to the base fluid such that the resulting water-in-oil emulsion, also referred to as an invert emulsion, may contain up to about 30-40 weight % internal aqueous phase based on the weight of the emulsion. The symbol “%” represents the term “percent” throughout this application.
During the drilling process, the drill bit generates drill cuttings as it forms the well bore. Drill cuttings consist of small pieces of shale and rock. The drill cuttings are carried in a return flow stream of the drilling fluid back to the well drilling platform. They are then separated from the bulk of the drilling fluid via conventional separators such as shale shakers, mud cleaners, and centrifuges. Some shale shakers filter coarse material from the drilling fluid while other shale shakers remove finer particles from the drilling fluid. After removing the drill cuttings therefrom, the drilling fluid may be re-used in the drilling process.
The drill cuttings separated from the bulk drilling fluid typically are discharged from the drilling platform to the surrounding area. Drilling platforms are often located offshore in hundreds of feet of water filled with marine life. The drill cuttings thus accumulate in the seabed near the base of the platform. Unfortunately, the drill cuttings collected from drilling with non-aqueous drilling fluids are contaminated with the oily organic drilling fluid. This oil must be removed from the drill cuttings before their disposal. Otherwise, the oil would pollute the surrounding environment and would be particularly hazardous to marine life.
The crude oil recovered from the subterranean formations often contains sand that must be separated from the oil. Like the drill cuttings, the sand is disposed of by dumping it from the drilling platform into the seabed where it forms sand piles. The sand also may be undesirably coated with the produced crude oil. Thus, the sand could adversely affect the marine environment unless the oil is removed therefrom.
Several methods have been used to remove oil from drill cuttings and sand to meet certain regulations designed to protect the environment from oil pollution. In one method, the oil is extracted using solvents such as toluene or methylene chloride. However, the potential hazards caused by the toxic nature of the solvents have raised doubts about this method. Another method involves transporting the drill cuttings and the sand onshore and subjecting them to a thermal process. For example, the oil is commonly burned off using very high temperature heat lamps or steam. Using such a thermal process can be very expensive, particularly since it is necessary to transport the drill cuttings and the sand to an onshore location.
As such, there continues to be a need for improved processes that utilize environmentally friendly, economical, and simple means for reducing the oil level in well bores, drill cuttings, and sand. The present invention utilizes a non-hazardous and simple process to remove oil contamination from solid materials, thus allowing for the drill cuttings and the sand to be inexpensively disposed of onsite, e.g., at the drilling platform.